PSI - Issue 19

534 Zhu Li et al. / Procedia Structural Integrity 19 (2019) 528–537 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 7 and N i,j,k can be determined by introducin g i index such that i=1… u . Thus, total fatigue damage index for u PSD positions can be calculated on the basis of Miner’s rule in Eq. ( 8). The total (fatigue damage index) FDI can be formulated as the summation of the damages that can be induced by each of the v PSD segments and each of the u PSD position s. According to Miner’s rule, total fatigue damage i.e. FDI is obtained by Eq. (8). D = ∑ =1 = ∑∑∑ , , − , , 5 =1 =1 =1 (8) 4. Discussion and Results The test bracket shown in Fig. 5 is designed such that two different small blocks (527 g, 254 g and 0 g) were mounted on the bracket to achieve three different natural frequency (40 Hz, 60 Hz and 112 Hz) of the brackets. The bracket material made of 5052-H32 aluminum alloys is selected, and monotonic and cyclic properties of the 5052 H32 aluminum alloy are given in Table 2.

Fig. 5. bracket configuration with added weights to obtain natural frequencies of 40,60 and 112 Hz for three different bracket samples; (b) a schematic representation of sample brackets.

Table 2. Material Properties of Aluminum 5052-H32. Monotonic properties Yield strength

193 MPa 228 MPa 70.3 GPa

Ultimate strength

Modulus of elasticity Elastic Poisson’s ratio

0.33

Density

2.68 g/mm3

Cyclic properties Material constant of S-N curve, C

1348 MPa

Slope of S-N curve, b

-0.17

Modal tests were conducted on test bracket to determine a natural frequency of the bracket components as a part of the model validation. The computed natural frequencies obtained from the FE modal analysis agree well with the experimental frequencies obtained from the modal test as provided in Table 3. The FE modal results are compared with experimental frequencies in Table 3 and error values between the FEA and the test is found to be in range of approximately 4-7%. The PSD spectrum tests could not be carried out because of missing appropriate software package for the shaker controller to conduct the time-varying PSD testing. Therefore, FEA spectrum analysis was